## Seismograph: Vertical (slow motion)

### How does a seismograph record the incoming P and S waves?

Generalized P and S-wave behavior are shown on this simplified model of a vertical-component seismograph station. Animation of the principles of a drum-style vertical seismograph station that records up-and-down movement. Seismographs are designed so that slight earth vibrations move the instrument. The suspended mass remains at rest as the spring absorbs some of the motion. The stylus (pen) affixed to the mass, records the relative motion between itself and the rest of the instrument, thus recording the ground motion. Animation shows compressive behavior of the P wave in the direction the wave is traveling and the shearing behavior of the S wave perpendicular to the direction of wave travel. Although the arrow shows gross movement, remember that this happens on a microscopic scale in the Earth.

#### Keypoints:

• Drum-style vertical seismograph station records up-and-down movement.
• Seismographs are designed so that slight earth vibrations move the instrument.
• The suspended mass remains at rest as the spring absorbs some of the motion.
• The stylus (pen) affixed to the mass, records the relative motion between itself and the rest of the instrument, thus recording the ground motion.

Level: Novice

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